To make the green herb dressing, combine all ingredients in a small food processor. Season with salt and pepper. Process until finely chopped.
Heat 1 tbs oil a large frying pan over medium-high heat. Add asparagus and cook, turning occasionally, for 3-4 minutes until just tender. Transfer to a serving plate.
Add remaining 1 tbs oil to the pan and heat over medium-high heat until hot. Add haloumi and cook for 1 minute on each side until just golden
and hot. Halve asparagus lengthways. Arrange asparagus, haloumi, tomatoes and onion on a serving platter. Drizzle with the green herb dressing.