Place the asparagus spears and olive oil into a bowl and stir to coat. Heat an ovenproof griddle pan until smoking hot, add the asparagus, garlic, thyme, chilli flakes, and season, to taste, with salt and freshly ground black pepper. Griddle for 2-3 minutes. Transfer the griddle pan into the oven and roast for eight minutes.
To serve, pile the roasted asparagus and garlic into the middle of a serving plate, top with a small pile of herbs and drizzle with balsamic vinegar and extra olive oil.