Combine onion, canola oil, and garlic in a large skillet. Cook over medium-high heat for 4 minutes. Add carrots, cauliflower, broccoli, and mushrooms one at a time with 2 minutes between each. Pour in soy sauce and stir to coat. Cook for 2 minutes more. Add water, tomato, basil, salt, and pepper. Bring to a boil; reduce heat and simmer until vegetables are fork-tender but not soft, about 5 minutes. Sprinkle with sunflower seeds.