Cook 1 1/2 cups pearl couscous in boiling salted water, 4 to 5 minutes; drain. Cook 1 small diced red onion, 3 chopped garlic cloves and 1 teaspoon chopped rosemary in olive oil in a large skillet over medium-high heat until softened, 4 minutes. Add 1 cup packaged strained tomatoes, 1/4 cup water and 1/2 teaspoon kosher salt. Simmer until thick, 5 minutes. Stir in the couscous and 1 tablespoon chopped parsley; season with salt and pepper. Top with more parsley.