Preheat the oven to 375°F (190°C).
Place the raw chicken and chopped mushrooms in a baking sheet or casserole dish; drizzle with 1 Tbsp oil and 2 Tbsp lemon juice, then sprinkle with 1/2 tsp salt (and pepper to taste), 2 tsp onion powder, and 1 tsp garlic powder. Toss to coat evenly.
Roast the chicken and mushrooms at 375°F for 30–35 minutes, until the chicken reaches an internal temperature of 165°F (74°C).
Remove from the oven and let cool slightly, then chop the chicken into bite-size pieces; set the chicken and roasted mushrooms aside.
Increase the oven temperature to 425°F (220°C). Roll out the 1 lb pizza dough on a 12-inch pizza tray.
Pre-bake the crust for 10–15 minutes, until it feels slightly firm and begins to brown.
Spread 1/2 cup pesto sauce evenly over the par-baked crust, then arrange the baby spinach leaves on top of the pesto.
Sprinkle the grated mozzarella evenly over the spinach, then distribute the chopped roasted chicken and mushrooms across the pizza.
Bake the pizza at 425°F for 10–15 minutes, until the crust is golden-brown and the cheese is melted and starting to brown.
If you prefer a crispier, more browned top, broil on high for 2–3 minutes—watch closely to avoid burning.
