Pre-heat the broiler. Broil the poblanos until blackened, 10 minutes. Transfer to a bowl, cover and let cool. Peel, seed and chop the poblanos.
Pre-heat the oven to 400°F.
On a baking sheet, toss the tortilla strips with 1 tablespoon oil and the cumin. Bake until golden, about 10 minutes; season with salt.
Meanwhile, in a large, deep skillet, heat the remaining 2 tablespoons oil over medium-high heat. Add the corn and cook until charred at the edges, 10-12 minutes. Add the red onion and garlic, season with salt and pepper and cook until the onion is softened, about 5 minutes. Stir in the stock, tomatoes and poblanos.
Divide the tortilla strips among four soup bowls. Add the avocado and a squeeze of lime juice. Ladle the soup over the avocado. Top with cilantro; serve with the sour cream.