Line a baking pan with parchment paper and lay the fish fillets on the pan in a single layer.
Mix oil, garlic powder, onion flakes, salt, dry thyme and chilli flakes in a small bowl, brush this onto both sides of the fish and bake for 8-10 minutes until the fish flakey and opaque. Remove from oven and set aside.
Mix the avocado, red onion, cherry tomatoes in a medium size bowl and squeeze in the juice of one lime adding salt to taste.
Layout the fish, avocado salsa, chopped lettuce, chopped coriander, tacos and sauce and let everyone assemble their own. Be messy and enjoy!