Whisk the garlic, cumin, lime and oranges juices and 1/2 teaspoon salt together in a medium bowl. Add the steak, coat well in the mixture and let marinade for 10 minutes.
Lightly oil the grill grates. Grill the steak, flipping once, until medium rare, 2 to 6 minutes per side depending on the thickness. Remove to a cutting board and let rest 5 minutes. Slice the steak against the grain and reserve.
Lay a tortilla on a work surface and top evenly with 1/2 cup pepper-jack cheese. Add 1/4 of the steak and some chopped chipotle in adobo and sauce. Fold the tortilla in half to enclose fillings. Repeat with remaining tortillas and ingredients.
Melt 1/2 tablespoon butter in a large nonstick or cast-iron skillet over medium heat. Cook the quesadilla, flipping once, until the cheese is melted and it is golden brown on both sides, about 3 minutes per side. Remove to a cutting board and repeat with the remaining quesadillas.
Cut into triangles and serve with guacamole, salsa, scallions and sour cream.
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