Heat the oven to 200°C (400°F). Line a baking tray with baking paper. Toss the sweet potato cubes with 1 tablespoon olive oil, 1 teaspoon smoked paprika, salt, and pepper. Spread them in a single layer and roast for 25 minutes, turning once halfway, until the edges are browned and a fork goes in easily.
While the sweet potatoes roast, heat 1 tablespoon olive oil in a large pot over medium heat. Add the onion and cook for 5 minutes, until soft.
Stir in the garlic, cumin, smoked paprika, and chipotle chilli powder. Cook for 30 seconds, until fragrant. Toasting the spices in the oil brings out their flavour.
Pour in the fire-roasted tomatoes and vegetable stock. Stir in the black beans. Bring to a gentle simmer and cook for 15 minutes.
Take the pot off the heat. Blend about half the soup with a stick blender, straight in the pot, until smooth. Leave the rest chunky. The half-blended soup stays thick without any cream.
Stir in the roasted sweet potatoes and lime juice. Warm the soup gently for 5 minutes. Taste and add salt, pepper, or more lime juice if needed.
While the soup warms, toss the tortilla strips with a little oil and salt and bake them at 200°C (400°F) for 5 to 7 minutes, until crisp and golden. Serve the soup hot, topped with tortilla strips, diced avocado, and fresh coriander.