Optional step: Heat the oil in a large skillet, then add the onion, peppers, and carrots. Sweat the vegetables for about 5 minutes, until they start to soften. Add the garlic and cook it with the vegetables for about 1 minute, until very fragrant, stirring constantly.
Place all ingredients into a large (5 quart or larger) slow cooker. Stir to combine.
Cover and cook on high for about 3 hours, or on low for about 5 hours, until the sauce is thick and the vegetables are tender.
Turn off the heat and season the chili with salt and pepper to taste.
Ladle into bowls and serve.
