Crock Pot Low-Carb Soup

Ingredients:

1 lb ground beef
1 onion, chopped
3 cloves garlic, minced
1 red bell pepper, chopped
1 green bell pepper, chopped
2 zucchinis, chopped
1 can diced tomatoes (14.5 oz)
4 cups beef broth
2 teaspoons chili powder
1 teaspoon cumin
Salt and pepper to taste
Optional toppings: shredded cheese, sour cream, sliced green onions