In the bowl of a food processor or blender, combine the avocado, yogurt, garlic, lime juice, cilantro, water, salt and pepper. Blend until smooth.
The Potatoes:
Bring a large saucepan of lightly salted water to a boil over high heat. Add sweet and russet potatoes and cook until just tender, about 5 to 8 minutes. Drain.
Heat the olive oil in a large skillet (preferably cast-iron) set over medium-high heat.
Add garlic and cook for 1 minute, stirring frequently.
Stir in the cooked sweet and russet potatoes and salt. Cook, stirring occasionally, until the potatoes start to brown, 8 to 10 minutes.
Stir in the black beans, bacon and cilantro.
Divide between 8 plates and top with each portion with 1 tablespoon of the avocado sauce.