In a shallow dish, combine 2 tbsp flour, 1/2 tsp garlic powder, 1/2 tsp salt, and 1/2 tsp pepper. Dredge each chicken cutlet in the flour mixture, coating both sides and shaking off any excess.
Heat 1 tbsp olive oil in a large skillet over medium-high heat until the oil shimmers.
Add the coated chicken cutlets to the skillet in a single layer (work in batches if they won’t fit without crowding). Cook the chicken 3–4 minutes per side, until golden and cooked through. Transfer the cooked chicken to a plate and set aside.
Reduce the heat to medium, add 1 tbsp butter to the same skillet and let it melt.
Add 1 lb sliced mushrooms, 3 cloves pressed garlic, and the additional 1/2 tsp salt to the skillet. Cook, stirring occasionally, until the mushrooms have reduced in size and any released liquid has mostly evaporated, about 4–6 minutes.
Pour in 2 cups heavy cream and stir in 1/2 cup grated Parmesan cheese until combined.
Bring the sauce to a gentle boil, stirring regularly, and cook for 2 minutes. Then reduce the heat to low.
Return the chicken cutlets to the skillet, nestling them into the creamy mushroom sauce. Simmer on low for 3–5 minutes, spooning sauce over the chicken, until the sauce has thickened and the chicken is heated through.
Remove from heat and serve the chicken with the mushroom cream sauce spooned over each piece.