Set up the slow cooker: Use a 5-quart (or larger) slow cooker so there’s enough room to stir later without spilling. If your slow cooker runs hot, plan to check at the earlier end of the cook time.
Start with the chicken: Place the chicken breasts in the bottom of the slow cooker in an even layer. If they’re very thick, you can cut each breast in half lengthwise so they cook more evenly and shred more easily later.
Season directly in the pot: Sprinkle garlic powder, dried oregano, and cracked black pepper evenly over the chicken. Try to cover the surface so the seasoning flavors the whole filling while it cooks.
Layer the aromatics and veggies: Add the sliced onion over the chicken, spreading it out so it softens evenly. Pour the frozen mixed vegetables on top. Keep the veggies on the top layer—this helps them cook gently and keeps the chicken from sitting above the liquid.
Mix the creamy base until smooth: In a large bowl, whisk together cream of chicken soup, cream of celery soup, and chicken broth. Whisk for 30–45 seconds until there are no streaks or thick lumps. This step matters because a smooth base gives you a consistent, creamy filling (no “pockets” of soup).
Add the sauce without stirring: Pour the soup-and-broth mixture evenly over the vegetables and chicken. Do not stir yet. Let the sauce settle down through the layers while cooking—this helps everything heat evenly and prevents the chicken from breaking apart too early.
Cook low and slow: Cover and cook on LOW for 6–8 hours or on HIGH for 4–5 hours. The chicken is ready when it reaches 165°F / 74°C and shreds easily with a fork. If the chicken feels firm or rubbery when you try to shred it, it needs more time—continue cooking and check again in 20–30 minutes (LOW) or 10–15 minutes (HIGH).
Shred the chicken properly: Remove the chicken to a plate (or shred right in the slow cooker). Use two forks to pull it into bite-size strands. Smaller shreds blend into the filling better and make each spoonful feel more “pot pie” and less like big chunks of chicken.
Stir to combine and check the texture: Return shredded chicken to the slow cooker (if removed) and stir thoroughly until the filling is evenly creamy and the vegetables are distributed. At this point, the filling should be thick enough to coat a spoon. If it seems too loose, see the next step.
Optional thickening (choose one): If you want a thicker, more “classic pot pie” texture, either (1) cook uncovered on HIGH for 20–30 minutes, stirring once halfway, or (2) stir in a cornstarch slurry (1 tbsp cornstarch mixed with 2 tbsp cold water) and cook on HIGH for 10–15 minutes until thickened. Add slurry slowly and stir well so it doesn’t clump.
Optional extra-creamy finish: For a richer filling, stir in 1/2 cup heavy cream after shredding and combining. Keep the slow cooker on WARM for 5–10 minutes so it blends in smoothly. Taste and add a pinch of salt if needed (soups and broth vary in saltiness).
Bake the biscuits separately: While the filling rests on WARM, bake the refrigerated biscuits according to the package directions until golden brown. Baking separately keeps them flaky and prevents sogginess.
Serve like a pot pie bowl: Spoon the creamy chicken-and-vegetable filling into bowls and top each serving with a warm biscuit (or split the biscuit and spoon filling over it). For the coziest bite, crack the biscuit open so the sauce soaks in.