Prep the tuna. Drain tuna thoroughly to prevent soggy pinwheels. Use a fork to break it into small flakes in a medium mixing bowl.
Make the dressing. Stir in Greek yogurt, mayonnaise (if using), Dijon, lemon juice, garlic powder, salt, and pepper. Taste and adjust seasoning.
You want a creamy but not runny mixture.
Add the crunch. Fold in celery, red bell pepper, red onion, and herbs. This adds texture and freshness without extra calories.
Lay out the tortillas. Place a tortilla on a cutting board. Scatter a small handful of spinach evenly over the surface, leaving a 1-inch border at the edges.
Spread the filling. Spoon half of the tuna mixture over the spinach and spread gently with a spatula.
Keep an even layer for clean slices.
Roll it tight. Starting from the edge closest to you, roll the tortilla snugly into a log. Tightness matters for neat pinwheels.
Chill (optional but helpful). Wrap the roll in plastic and refrigerate for 10–15 minutes to firm up. This step makes slicing much easier.
Slice. Using a sharp serrated knife, trim off the ends, then cut into 1-inch pieces. Repeat with the second tortilla and remaining filling.
Serve. Arrange on a platter.
Add a squeeze of lemon and a sprinkle of herbs or seasoning for a fresh finish.