Slice the chicken breasts in half horizontally to create four thin cutlets of even thickness.
Season both sides of the cutlets evenly with garlic powder, half a teaspoon of salt, and half the black pepper.
Heat one tablespoon of olive oil and the butter in a large 12-inch skillet over medium-high heat until hot and sizzling.
Add the chicken cutlets in a single layer and sear for 3 to 5 minutes per side until golden and cooked through to 165°F.⏱ 5 min
Transfer the cooked chicken to a plate and set aside.
Add the remaining tablespoon of olive oil and sliced mushrooms to the skillet over medium heat.
Sauté the mushrooms for 5 to 7 minutes, stirring occasionally, until they release liquid, soften, and turn deeply golden brown.⏱ 7 min
Add the sun-dried tomatoes and minced garlic to the skillet, stirring constantly for 1 minute until fragrant.⏱ 1 min
Pour in the heavy cream and bring to a gentle simmer over medium-low heat.
Stir in the grated Parmesan cheese and the remaining salt and pepper, simmering for 2 minutes until slightly thickened.⏱ 2 min
Add the fresh spinach and stir for about 1 minute just until the leaves begin to wilt.⏱ 1 min
Return the chicken cutlets to the pan, spooning the warm sauce over them to coat before serving.