Preheat a grill to medium-high. In a bowl, toss the cabbage with half of the lemon juice and season with 1 teaspoon each salt and pepper. Microwave the bacon on a paper towel- lined plate on high heat until crisp, about 4 minutes; crumble.
Grill the tortillas, turning once, until lightly charred, about 3 minutes; wrap in a kitchen towel to keep warm.
Meanwhile, in a bowl, toss the scallions with 1 tablespoon olive oil and season with salt and pepper. Grill, turning, until slightly charred, 3 to 5 minutes. Using the same bowl, toss the chicken with 2 tablespoons olive oil and season with salt and pepper. Grill, turning once, until cooked through, 6 to 8 minutes. Let the chicken rest for 5 minutes before thinly slicing along with the scallions.
In a small bowl, add the remaining lemon juice and slowly whisk in the remaining 1/4 cup olive oil; season with salt and pepper. Stir in the sliced scallions and the apple. Divide the chicken among the tortillas and top with the vinaigrette and bacon. Serve with the sour cream and slaw.