How to Make It
Thinly slice white parts of scallions; set aside green tops. Combine white scallion slices, sugar, soy sauce, chili garlic sauce, 2 tablespoons rice vinegar, garlic, and 1 tablespoon sesame oil in a large ziplock plastic bag. Seal bag, and gently shake to combine. Add steak, and seal bag. Massage bag to coat steak with marinade. Chill 12 hours or up to 1 day. Remove steak from bag; discard marinade.
Stack 5 wonton wrappers on top of each other. Using a pizza cutter, cut wonton stack diagonally into quarters to form wedges. Repeat procedure with remaining 5 wonton wrappers.
Heat 2 tablespoons sesame oil in a large skillet over medium-high. Place half of wonton wedges in hot oil; cook, stirring occasionally, until crisp and browned, 1 to 2 minutes. Using a slotted spoon, transfer fried wonton wedges to a paper towel–lined plate to drain. Repeat procedure with remaining half of wonton wedges.
Heat a grill pan over high, and lightly coat with cooking spray. Add steak to pan; cook to desired degree of doneness, 2 to 4 minutes per side for medium-rare. Let stand at least 5 minutes, and cut against the grain into thin slices.
Whisk together remaining 2 tablespoons rice vinegar; remaining 1 tablespoon sesame oil; gochugaru, if desired; and salt in a medium bowl. Cut green scallion tops into 2-inch pieces, and cut each piece in half lengthwise. Add green scallion slices and bok choy to dressing; toss to coat. Divide bok choy mixture evenly among 4 bowls. Top evenly with kimchi and daikon. Divide steak slices, fried wontons, and avocado evenly among bowls.