Place the asparagus in a baking pan. Don’t worry about finding a pan large enough to hold the asparagus in one layer – the stalks can overlap a bit. Drizzle the olive oil over them and toss gently to coat the asparagus evenly. Sprinkle on the salt, and toss again.
Roast the asparagus for 7 to 10 minutes for thin stalks, 10 to 14 for thick ones. Remember that they will continue to cook a bit after you remove them from the oven, so take them out while they’re still a little firmer than you would like. Transfer to a plate and let cool to room temperature.
Meanwhile stir together the mayonnaise, olive oil, rice vinegar, parsley, oregano and mustard. Season with salt and pepper.
Drizzle the sauce over the asparagus and serve at room temperature.