Preheat grill on HIGH 10 min. Combine ground turkey, baby spinach, bread crumbs, feta, oregano, cracked pepper, and olive oil in mixing bowl. Divide mixture into fourths; form 4 burgers.
Coat cleaned grill grate lightly with vegetable oil. Place burgers on grill. Reduce heat to MED.
Sear burgers on grill 2 min, until they have changed color about one-quarter of way up from bottom. Turn over; sear 2-3 min. Turn again; reduce heat to MED-LOW. Close lid.
Cook 8-10 min until internal temp reaches 165 degrees (check by inserting thermometer halfway into thickest part of burgers). Transfer to clean platter.
Top each burger with 1 Tbsp tzatziki, 3 or 4 roasted red pepper strips, and 3 slices cucumber. Serve on rolls.
