To prepare the leek, cut off the coarse green part on the top of the leek and cut off the root. If the outer layer is also coarse, peel that off. Discard those parts or use for stock.
Cut the leek in half length-wise and then lay it on the flat sides to slice into half moons. Toss these into a small bowl of cold water and gently break apart with your hands, so all the dirt and grit fall to the bottom of the bowl.
To prepare the asparagus, cut off the tough bottoms then slice the asparagus on the diagonal.
In a large, oven-proof pan, heat the olive oil over medium heat. Using a slotted spoon, remove leaks from the water, shaking off excess water, and place them into the pan. Add the carrots, asparagus, peppers and mushrooms and sauté for about 10 minutes until the veggies are golden and any water is cooked out.
Season the veggies with the salt and pepper and then stir the spinach into the veggie mixture until wilted and the water is cooked out. The pan will be very full, so you might have to add the spinach in stages.
In a bowl, whisk together the eggs and ricotta cheese.
Spread out the veggies evenly in the pan. Give the pan a light coating of cooking-spray. Pour the egg mixture over the top and swirl it around the pan so it is even.
Sprinkle the Parmesan cheese over the top and bake for 30-35 minutes until the frittata is puffed up and golden on the top. Let cool for 5 minutes before serving.