Mix together the paprika, brown sugar, chili powder, cumin, chipotle chile powder, garlic powder and 1 teaspoon salt in a small bowl. Toss the chicken in a container with the oil and lime juice, then rub with the spice mixture. Refrigerate, covered, for at least 30 minutes up to 2 hours before cooking.
Heat the oil in a large nonstick skillet over medium-high heat. Add the mushrooms and cook, stirring occasionally, until brown and tender, about 5 minutes. Add the butter, cumin, corn kernels, poblano and 1/4 teaspoon salt and cook until the corn is light brown, about 3 minutes. Stir in the scallions and lime juice and season with salt. Set aside.
Prepare an outdoor grill for medium-high heat.
Lightly brush the grill grates with oil. Grill the chicken breasts until marked and cooked through, 5 to 6 minutes per side. Transfer to a cutting board, let rest for 10 minutes and then thinly slice.
Serve with the warm tortillas, corn and mushroom topping, chopped cilantro, guacamole, sliced pickled jalapenos, lime wedges, shredded pepper jack cheese, salsa, chopped scallions and sour cream.
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