Grind peppercorns, coriander seeds and fennel seeds to fine powder. Lightly spray steak with nonstick spray; sprinkle each side with salt, pepper and 1-1/2 teaspoons spice mix. Let stand 30 minutes.
Prepare barbecue (medium-high heat). Grill steak until cooked to desired doneness, about 2-1/2 minutes per side for medium-rare, transfer steak to cutting board and keep warms. Let rest 10 minutes.
Meanwhile, spray asparagus and onion slices with nonstick spray; sprinkle with salt and pepper. Grill asparagus until crisp-tender and slightly charred, turning often, about 5 minutes. Transfer asparagus to plate. Keeping slices intact, grill onion until slightly charred and almost tender, about 4 minutes per side; transfer to plate with asparagus.
Cut steak crosswise into slices. Arrange steak and asparagus on 6 plates. Drizzle with lemon vinaigrette. Garnish salads with some onion rings and orange slices.