Halve each zucchini lengthwise; cut crosswise 1/2 inch thick. Quarter and seed the bell peppers; cut into about 16 pieces. Transfer to a bowl and add the tomatoes. Drizzle with 2 tbsp. EVOO; toss.
Cut the pork crosswise into 6 slices; cut each slice into 6 chunks and transfer to another bowl. Add the remaining 2 tbsp. EVOO; crumble the oregano on top. Place a fine grater over the bowl and grate the garlic onto the pork. Squeeze the juice from the lemon wedges over the pork. Mix well with a rubber spatula, cover and refrigerate for 20 minutes.
Preheat a heavy grill pan or a grill over medium-high heat. Meanwhile, on each of 8 skewers, thread about 6 vegetable chunks, alternating zucchini, pepper and tomato as you wish. Thread 4 or 5 chunks of pork onto each of the remaining 8 skewers.
Season all skewers with salt and pepper. Grill, covered, until marked on the bottom, about 2 minutes; flip with a metal spatula. Cover and cook until the pork is just firm, about 2 minutes, and the vegetables are crisp-tender, about 4 minutes.