How to Make It
Heat 1/2 cup oil in a 12-inch cast-iron skillet over medium. Working in batches, fry plantain slices until light golden, 1 minute and 30 seconds to 2 minutes per side. Transfer plantain slices to a cutting board; smash to 1/8-inch thickness using bottom of a measuring cup.
Working in batches, return smashed plantain slices to hot oil; fry over medium until golden brown and crisp, 30 seconds to 1 minute per side. Transfer plantain slices to a baking sheet lined with paper towels.
Sprinkle fried plantain slices evenly with 1/2 teaspoon salt. Let cool 10 minutes.
Meanwhile, whisk together vinegar, sumac, mustard, molasses, pepper, remaining 1/4 cup oil, and remaining 1 teaspoon salt in a large bowl. Add greens; massage mixture together with your hands until collards are wilted and tender, 1 to 2 minutes. Let stand 10 minutes.
Add sliced fennel bulb, apples, and shallots to collard mixture; toss to coat. Add plantains; fold once to incorporate. Transfer to a serving platter; sprinkle with reserved chopped fennel fronds.
Fried plantains may be substituted with 1 cup store-bought plantain chips (about 1 1/2 ounces). Follow recipe as directed, omitting steps 1 through 3.