Melt the butter in a small skillet, stir in the herbs, lemon zest and crushed red pepper flakes. Keep warm over low heat.
Steam the corn until crisp-tender, then cut each ear into 4–5 rounds.
Thread the sausages, onion wedges, shishito peppers and corn onto metal skewers. Brush some of the herb butter onto the skewers. Grill the skewers until vegetables are crisp tender and sausages are browned and hot, brushing more butter on as they grill and after they come off the grill. Serve at once.