Preheat the oven to 400°F. Cut the sweet potato (no need to peel) into rounds about 1 inch thick. Place them on a baking sheet and toss with 2 tsp vegetable oil and a pinch of salt and pepper. Roast until tender, about 18 to 20 minutes.
Halve the grape tomatoes. Peel and chop the orange, removing any seeds. Peel and dice the red onion. Roughly chop the cilantro stems and leaves. In a large bowl, mix together the tomatoes, orange, just 2 tbsp diced red onion, just half the cilantro, and a pinch of salt and pepper. Halve the lime and cut half into wedges. Add the juice from just half the lime to the salsa and toss the citrus salsa.
Place a large nonstick skillet over medium-high heat with 2 tsp vegetable oil. Once hot, add the cauliflower rice and a pinch of salt and pepper and cook, stirring occasionally, until tender and brown in places, about 5 to 6 minutes.
Drain and rinse the black beans. Place a small saucepan over medium-high heat with 2 tsp vegetable oil. Add the remaining diced red onion and just 1½ tsp taco seasoning and cook until softened, about 3 to 4 minutes. Add the black beans and ¼ cup water and cook until hot, about 3 to 5 minutes. Mash some of the beans the back of a fork.
In a small bowl, mix together a pinch of the remaining taco seasoning and the ranch. Taste and add more taco seasoning until the sauce is to your liking.
Divide the cauliflower rice between large shallow bowls. Top with the roasted sweet potatoes, citrus salsa, and mashed black beans. Sprinkle with remaining chopped cilantro, serve with lime wedges and spicy ranch sauce for dipping.