Preheat the oven to 375°F.
Cook the spaghetti according to package directions for just under al dente. Drain the pasta then return it to the cooking pot and set aside.
Into a large skillet over medium-high heat, add the olive oil. When the oil is hot, crumble the vegan ground beef into the pan. Use a spatula to break up any clumps. Add the onion and cook for 5 minutes, stirring frequently until meat is browned.
Add the garlic and Italian seasoning then continue cooking for an additional 1 minute.
Add the diced tomatoes and spaghetti sauce, stirring to incorporate. Simmer for 5 minutes.
Pour the sauce mixture into the pot with the cooked spaghetti. Toss to coat all of the noodles with sauce.
Transfer to a prepared 9x13-inch baking dish. Sprinkle the mozzarella and Parmesan cheeses over the top.
Bake for 30 minutes then serve hot.