Chop onions, bell peppers, and zucchini. Peel and chop sweet potato. Finely chop garlic. Set aside.
Heat oil in large nonstick skillet over medium-high heat.
Add beef; cook, stirring frequently, for 5 minutes, or until browned. Add onion and garlic; cook, stirring occasionally, for 5 minutes, or until onion is translucent; remove from pan.
Transfer beef mixture to slow cooker; add bell peppers, zucchini, sweet potato, tomatoes, water, chili powder, cumin, onion powder, oregano, salt, and pepper.
Cover and cook on low heat for 7 to 8 hours (or high heat for 4 to 5 hours).
Divide evenly among four bowls; garnish with cilantro (if desired). Store unused portion refrigerated in an airtight container for up to 4 days.
The Nutrition Facts box below provides estimated nutritional information for this recipe.