If needed, pour out and discard any excess fat from pan, then stir in zucchini. Cook, stirring occasionally, until slightly softened, about 5 minutes. (TIP: If pan seems dry, add another drizzle of oil.) Add garlic, tomato paste, and Italian Seasoning. Cook, stirring, until fragrant, 1-2 minutes. Add tomatoes and their liquid, stock concentrate, 1 cup water, salt, and pepper. Bring to a boil, then reduce heat to low. Cook, stirring, until slightly thickened, 3-4 minutes. Season with salt and pepper.