Remove the wire rack from your oven. Preheat the oven to 200°C/Fan 180°C/Gas 6. Lay each tortilla over 2 bars of the wire rack. Most of the wrap should hang down through the bars to make scoops. This will give you crisp tortilla taco shells.
Slide the rack into the oven and bake the tortillas for 5 mins, till crisp and slightly golden. Carefully remove the taco shells and place them on a plate. Turn the oven off. Set the grill to a medium heat.
Line a baking tray with foil. Snap the woody ends from the asparagus. Cut the tender asparagus spears in half. Cut the portobello mushrooms into 1cm-thick slices. Cut any large shiitake mushrooms in half, leaving the smaller ones whole. Peel and thinly slice half the onion. Tumble everything on to the foil-lined tray.
Peel and grate the garlic cloves into a small bowl. Mix with 2 tbsp olive oil and plenty of seasoning. Spoon the garlicky oil over the veg and use your hands to toss everything together.
Slide the tray under the grill for 10-15 mins till the veg is tender and slightly charred. Check it now and then to make sure it isn't burning. If the veg is cooked before you've finished making the salsa, turn the grill off and move the tray to a lower shelf to keep warm.
Meanwhile, make your avocado salsa. Peel and finely chop the remaining onion half and place it in a medium bowl. Zest and juice the lime into the bowl with a good pinch of salt. Scrunch together to begin marinating the onion.
Halve the avocado and scoop out the flesh. Discard the stone. Roughly chop the flesh and add to the bowl, tossing it in the onion and lime juice to stop it going brown. Finely chop the tomato and add that. Halve the chilli and flick out the seeds for less heat. Finely chop it and add to the bowl. Roughly chop the coriander and add most of it to the salsa. Mix everything together.
Remove the veg from under the grill. Divide the taco shells between 2 plates. Fill each with a small handful of coriander and rocket leaves. Add a spoonful of the avocado salsa to each, followed by the garlicky grilled veg. Spoon over the sweet chilli sauce and scatter over the remaining coriander to serve.