Cook shells according to package instructions, drain and set aside in the pot that the noodles cooked in.
Preheat oven to 425 degrees Fahrenheit. Line a large baking sheet with parchment paper. Add 12 cloves of the garlic (saving 3 for later), the onion, and zucchini to the sheet pan. Top with the olive oil, garlic powder, and garlic salt. Toss well to combine, making sure the vegetables are coated in the spices and oil. Place baking sheet in the oven and bake for 40 minutes, flipping the vegetables halfway through baking.
When vegetables are finished roasting, add them to a high speed blender with the remaining 3 cloves of raw garlic, soy milk, and the nutritional yeast. Blend until a thick and creamy sauce forms.
Pour sauce over the shell pasta in the pot, and heat on low heat until warmed through. Serve and enjoy!