In a skillet on medium heat, crumble sausage and cook until browned and almost cooked, about 5-8 minutes, turning occasionally to ensure even browning. Drain excess oil, if needed.
Add onions, mushrooms, italian seasoning, salt and tomato paste. Cook another 5-6 minutes, until onions are softened and mushrooms are cooked through.
Toss in chopped spinach and diced tomatoes. Stir and allow to come to a simmer. Cover and cook another 2-3 minutes, until spinach is wilted and everything is heated through.
Pour in cooked quinoa and combine thoroughly. Divide into bowls and top with cheese and pepper flakes.
Notes
Add 1/4 - 1/2 cup water if needed. One reader felt water was necessary. There was no additional water added when our chef prepared the recipe.