Cut the zucchini and yellow squash on a spiralizer using the medium size blade. If you don’t have a spiralizer, cut into thin rounds.
Bring a large pot of boiling water to a boil and add 1/2 t. salt. Cook the spaghetti 6-8 minutes until al dente. Do not drain. Do not over cook! Reserve 1 cup of the pasta water.
Heat a large stainless steel skillet over medium heat. Add the olive oil and swirl to coat.
Add the grape tomatoes and the remaining 1/4 t. salt. Cook 6 - 8 minutes until tomato skins begin to brown and split.
Using tongs, transfer the cooked spaghetti from the pasta water and into the skillet with the tomatoes. Add 1/2 cup of the reserved pasta water. Gently toss to combine.
Add the zucchini and yellow squash and gently toss to combine. Allow to heat through 2-3 minutes. If all the liquid evaporates, add more of the reserved pasta water.
Sprinkle with freshly ground pepper to taste.
Serve immediately. Using tongs, place one scoop of the hot spaghetti mixture onto a plate. Sprinkle with 1-2 tablespoons of grated Parmesan. Top with another scoop of the hot noodles and grated Parmesan.