1. Preheat oven to 400 degrees. Line a 9-by-13-inch baking pan with parchment paper.
2. Add pasta, veggies, nutritional yeast, and sauce to the baking pan. Stir well to mix then spread into an even layer. Pour water over the top then give the pan a shake or stir a bit to make sure the water is evenly distributed.
3. Cover the pan tightly with aluminum foil and bake for 35 to 40 minutes.
4. Uncover and stir in mayonnaise, then place back in the oven and broil another 5 minutes. Serve warm.