Preheat oven to 400°F – 200°C and set the rack about 6 inches (15 cm) from the top element.
In a small bowl, mix olive oil, cumin, paprika, chili, chipotle, garlic, salt, pepper and lime zest.
Place sweet potato rounds on a large roasting pan and brush both sides generously with the mixture. Roast for 20-25 minutes, or until just tender when pierced with a fork.
Meanwhile, make the smashed avocado by combining the avocado flesh, juice of the lime and a little salt. Use a fork to crush it.
Remove from the oven. Using the base of a glass or jar, gently press each round to flatten slightly. Don’t crush them completely, you want some height left for that creamy centre.
Spoon any leftover oil mixture over the tops. Switch the oven to broil (grill) and cook for 3–5 minutes, until the edges caramelise and slightly crisp. Keep a close eye, they can burn quickly.
Squeeze over fresh lime juice, sprinkle with flaky salt, and garnish with toasted sesame seeds and chopped coriander if desired.
Serve hot as a side, or top with smashed avocado, a spoon of Greek yogurt for a light meal.
