Cut chicken breast in half lengthwise. Sprinkle breast with salt, pepper, and oregano. Dredge the chicken in flour.
Add 2 tbsp oil to a pan. When hot add chicken, and cook over med-high heat until browned, about 5 minutes. Flip and cook for an additional 5 minutes on the other side. Remove chicken from pan.
Add 1 tbsp oil. Then add chopped onion, garlic, and pepper. Stir and cook for 3 minutes. Add sun-dried tomatoes, and tomato paste and stir well. Add spinach and once wilted add milk, parmesan, and salt and pepper. Return chicken to pan and heat through.