Preheat oven to 350°F and line a baking sheet with aluminum foil.
In a large pot over medium heat, cook ground beef, breaking apart, until cooked through. Drain grease from pot. Stir in 1 cup onion, 4 cloves minced garlic, chili powder, cumin, tomatoes and tomato paste. Reduce heat to low and simmer 20 minutes.
Arrange poblanos on baking sheet. Divide mixture among poblanos and top with cheese if using for Keto recipe. Bake until poblanos are tender and cheese has melted, about 20 minutes.
Meanwhile, heat oil in a large skillet over medium heat. Add garlic, remaining onion and zucchini to pan and cook until softened, about 4-5 minutes. Stir in cauliflower rice and cook until heated through. Add cilantro and combine in skillet. Season with salt and pepper to taste.
Divide prepared poblanos and rice among four plates and serve immediately.