Slow Cooker Vegan Chili

Name: Slow Cooker Vegan Chili
Prep time: 30 min
Cook time: 5 h 10 min
Total time: 5 h 40 min
Cuisine: TexMex
Ingredients: 1 tablespoon olive oil; 2 onions, chopped; 1 green bell pepper, chopped; 1 red bell pepper, chopped; 1 yellow bell pepper, chopped; 4 cloves garlic, minced; 2 (14.5 ounce) cans diced tomatoes with juice; 1 (15 ounce) can black beans, rinsed and drained; 1 (15 ounce) can garbanzo beans, drained; 1 (15 ounce) can kidney beans, rinsed and drained; 2 (6 ounce) cans tomato paste; 1 (10 ounce) package frozen chopped spinach, thawed and drained; 1 cup frozen corn kernels, thawed; 1 zucchini, chopped; 1 yellow squash, chopped; 6 tablespoons chili powder; 1 tablespoon ground cumin; 1 tablespoon dried oregano; 1 tablespoon dried parsley; 0.5 teaspoon salt; 0.5 teaspoon ground black pepper; 1 (8 ounce) can tomato sauce, or more if needed; 1 cup vegetable broth, or more if needed