Step 1: Light your wood oven and preheat to about 400 degrees.
Step 2: Cook the noodles: Bring 4 quarts of lightly salted water to a rapid boil in a large pot over high heat. Add the macaroni and cook until al dente, about 8 minutes, stirring occasionally. Drain the macaroni in a large colander, rinse with cold water until cool, and drain again. Toss the macaroni with the oil to prevent sticking.
Step 3: Set up the grill for direct grilling and preheat to high.
Step 4: When ready to cook, lightly brush the corn and onion with olive oil and season with salt and pepper. Grill the corn and onions until nicely browned, 2 to 3 minutes per side (8 to 12 minutes in all for the corn, and 3 to 4 minutes per side for the onion, turning with tongs as needed. Transfer to a cutting board and let cool. Grill the poblano chiles and red bell pepper until darkly browned, 3 to 4 minutes per side. Transfer to the cutting board and let cool.
Step 5: Cut the kernels off the corn and place in a mixing bowl. Dice the onions and core, seed, and dice the poblanos and bell pepper. Place in the mixing bowl as well.
Step 6: Melt the 2 tablespoons butter in a large saucepan over medium heat. Add the grilled vegetables and cook until sizzling, 2 minutes. Stir in the flour and cook for 1 minute. Stir in the half and half and increase the heat to high. Boil the mixture for 3 minutes, stirring well; it will thicken. Remove the pan from the heat and stir in the mustard and cooked macaroni, followed by the cheese. Add salt and pepper to taste; the mixture should be highly seasoned. Spoon the macaroni and cheese into the cast iron skillet. Sprinkle the top with the bread crumbs and drizzle the remaining 2 tablespoons melted butter over the breadcrumbs.
Step 7: Bake the mac and cheese in the wood-burning oven until the sauce is bubbly and the top is crusty and golden brown, about 40 minutes. Serve at once.
Step 8: Indirect grill method: Set up the grill for indirect grilling and preheat to medium-high. When ready to cook, place the macaroni and cheese in the center of the hot grate, away from the heat, and cover the grill. Toss the wood chips on the coals. Cook the macaroni and cheese until the sauce is bubbly and the top is crusty and brown, 40 minutes to 1 hour.