Step 1: In a large pot, bring 8 quarts of salted water to a rolling boil over high heat. Add the macaroni and cook until al dente, 7 to 8 minutes. Drain the macaroni in a large colander, rinse with cold water until cool, and drain again. Toss the macaroni with oil to prevent sticking.
Step 2: Light a wood-burning oven and preheat it to 400 degrees F or set up your grill for indirect grilling and preheat it to 400 degrees F.
Step 3: Lightly brush the onion quarters and corn with melted butter (you’ll need about 2 tablespoons) and season with salt and pepper. Roast in a baking dish until browned on all sides, 8 to 12 minutes in all, turning with tongs. Roast the chiles and peppers the same way. Alternatively, indirect grill the onion quarters and corn as well as the chiles, and peppers. Transfer the vegetables to a cutting board and let cool.
Step 4: Thinly slice the onion quarters crosswise. Cut the kernels off the corncobs. Scrape any burned skin off the poblanos and peppers and dice, discarding the stems and seeds. The recipe can be prepared a day ahead to this stage.
Step 5: Brown the bacon in 1 tablespoon of butter in a large saucepan over medium-high heat. Add the shallots and sauté until lightly browned. Stir in the onion, corn, chiles, and peppers. Whisk in the flour and cook for 1 minute. Increase the heat to medium-high and whisk in the half-and-half. Boil the mixture for 3 minutes, whisking constantly; it will thicken. Remove the pan from the heat and stir in the mustard and macaroni, followed by the cheese and lobster. Add salt and pepper to taste: the mixture should be highly seasoned. Grease a large cast-iron skillet with 1 tablespoon of the butter.
Step 6: Spoon the mac and cheese into the skillet. Mix the panko with the remaining 2 tablespoons of melted butter; sprinkle the panko on the mac and cheese.
Step 7: Place the mac and cheese in the wood-burning oven (or on the grill). Roast or indirect grill until the sauce is bubbly and the top is crusty and brown, 25 to 30 minutes. Serve at once directly from the skillet.