Boil salted water in a large pot and cook pasta until al dente. Reserve 1.5 cups of starchy pasta water before draining.
Pound chicken until evenly thick, then cut into 1/2 inch strips. Coat chicken with a mixture of flour, garlic powder, dried thyme, 1/2 teaspoon salt, and pepper.
Heat 2 tablespoons olive oil in a skillet and cook chicken until golden brown and cooked through. Set aside.
Deglaze the skillet with white wine, then add onion, sauté for 2 minutes. Add remaining olive oil, mushrooms, and cook for 3 minutes.
Stir in garlic, sun-dried tomatoes, and 1/4 cup beef broth. Cook for 2-3 minutes.
Add remaining broth, pasta water, and tomato paste. Bring to a gentle boil, then thicken the sauce.
Remove from heat, whisk in heavy cream, then return to heat. Add chicken and pasta to the sauce, toss until coated.
Adjust sauce consistency with additional pasta water if desired.
Garnish with Parmesan cheese and fresh thyme.