Season the sweet potato and beet with salt and pepper. Roast for 25-30 minutes, tossing halfway through.
While the vegetables are roasting, add the avocado, garlic, green onion, and olive oil to a food processor and blend for a few minutes until smooth. Add water if need to achieve a creamy consistency and season with salt, pepper, and basil.
Toss the romaine, black beans, roasted sweet potato, and roasted beet together in a large bowl with the avocado dressing. Serve immediately and enjoy!