Blend all sauce ingredients together at high speed in a blender to achieve a loose, uniform purée. Taste and adjust seasoning as needed.

Pat trout dry and salt and pepper each inside and out. Spoon 1-2 tablespoons sauce into each fish cavity, just enough to coat. Shingle lemon slices on top of the sauce down the length of the trout, 3-4 slices per fish. Using kitchen twine, carefully tie fish at the swell of each lemon to keep all as a tidy bundle as you grill.

Place lemon halves, garlic scapes, and asparagus in a metal roasting pan, drizzle generously with olive oil and season with kosher salt and freshly cracked pepper, and toss to combine.

Prepare a chimney for the grill. Remove grill grate and loosely bunch newspaper at chimney base. Fill with charcoal. Light paper in a few places to ignite the charcoal. Once flames subside coals will begin to glow. Once they begin to turn white, transfer charcoal into a pile at the center of the grill for direct grilling.

Replace grate, carefully spray with high heat cooking oil, and place fish in the center, nestling lemon halves, asparagus, and scapes around. Replace lid and grill undisturbed for 3-4 minutes. Carefully turn fish to second side – the first side should show some char – and grill for another minute or two. Turn scapes and asparagus as needed for a mixture of softened and charred spots. Gently transfer grilled fish to a serving platter. Arrange the grilled lemons and surround the lot with the tangle of grilled scapes and spears. Spoon additional green zippy sauce onto each fish and serve at once.