In the slow cooker, combine crushed tomatoes, vegetable or chicken broth, diced onion, minced garlic, diced carrots, diced celery, dried basil, dried oregano, salt, and pepper. Stir to mix well.
Cover the slow cooker and set to low heat for 4 hours.
After 4 hours, add the cheese tortellini and fresh spinach to the soup. Stir and cover again, cooking for an additional 20 minutes, or until the tortellini is tender.
Meanwhile, preheat your oven to 400°F (200°C).
Mix the softened butter and garlic powder in a small bowl. Spread this mixture over one side of each slice of bread.
Place the bread on a baking sheet, butter side up, and sprinkle shredded cheddar cheese evenly across the slices.
Bake in the oven for 10-12 minutes, or until the cheese is melted and bubbly, and the bread is toasted.
Serve the hot soup in bowls with Cheddar Toast Bites on the side or floating on top.