Cook pasta as per package instructions. Reserve 1/4 cup of pasta water and set aside. Drain pasta in a colander, apply some oil and set aside. In the meanwhile dice all your veggies and set aside.
Heat olive oil and butter in a heavy bottomed pan, add onions, mushrooms, and garlic. Saute on medium, heat for about 3-5 minutes until the mushrooms and onions are tender. Do not brown the garlic or onion.
Next add in the diced zucchini, yellow squash and bell peppers. Saute for about 5-7 minutes until the veggies are tender. Do not make them mushy. Depending on how big or small you have cut them, the veggies may take more or less time to cook. Try and maintain a uniform size for all of them.
Next add in tomatoes, Italian seasoning, red pepper flakes, freshly ground pepper and chopped basil. Cook for another 2 minutes until tomatoes are tender but not mushy.
Add in reserved pasta water. Let it cook until it heats through. Check for salt and adjust accordingly.
Toss in the pasta along with lemon juice. Mix well, switch off the heat. Sprinkle some more olive oil if desired & grated parmesan cheese before serving.