Combine chili powder, thyme, salt, and pepper in small dish. Set aside.
Heat oil in large skillet over medium heat. Add onion and garlic, and sauté 3 to 4 minutes, or until onion is translucent. Add chili powder mixture, and cook 30 seconds.
Add cauliflower, celery, and 1/3 cup water. Cover, and cook 4 minutes, stirring occasionally.
Add potatoes and bell pepper. Cover, and cook 3 to 4 minutes, or until cauliflower is crisp-tender. Add 2 to 3 Tbs. water during cooking if mixture becomes dry. Remove from heat. Stir in parsley, and serve.