Add the butter to a nonstick skillet and heat over medium-high heat. Once the butter is melted, add the onion. Cook, stirring occasionally, until the onion has slightly softened, 2 to 3 minutes. Add the garlic and stir to combine. Cook until the garlic is fragrant, about 30 seconds. Add the tomato paste, cumin and a generous pinch of salt and pepper. Stir to coat the onion mixture in the tomato paste and seasonings. Add the cauliflower rice and stir to coat. Cook, stirring occasionally, until the cauliflower rice is cooked through, 8 to 10 minutes. Season with salt and pepper and serve immediately.