Sausage Veggie Breakfast Casserole

Name: Sausage Veggie Breakfast Casserole
Ingredients: 1 tablespoon extra-virgin olive oil; 4 ounces breakfast sausage; 4 ounces sliced cremini mushrooms; 1 small leek, cleaned and chopped; 1 clove garlic, grated; 1/2 red bell pepper, seeded and diced; 1/4 teaspoon hot paprika; Pinch of ground mustard; Kosher salt and freshly ground black pepper; 8 ounces frozen chopped spinach, thawed and squeezed out; 4 large eggs; 1 to 2 dashes hot sauce; 3 ounces Gruyere cheese, grated; Nonstick cooking spray, for the ramekins