Mix the pesto with the plain Greek yogurt, minced garlic, and a pinch of salt and pepper.
Cut the bagels in half and, optionally, toast them. You can toast them in the toaster or in a frying pan over medium heat for a couple of minutes. If using a pan, you can use a dry pan or add 1/2 tbsp of butter or a drizzle of olive oil.
To a large frying pan or grill pan over medium heat, add 1 tbsp of oil. When the oil is hot, add the halloumi slices and pan-fry for about 2 minutes on each side until golden.
Prepare the halloumi bagel assembly board (toasted bagels, pan-fried/grilled halloumi slices, pesto-yogurt sauce, sliced tomatoes, thin slices or ribbons of cucumber, thin slices of red onion, and a pinch of salt and pepper).
Assemble the bagels. To each bagel, add pesto-yogurt sauce, a couple of tomato slices, thinly sliced red onion, cucumber ribbons, 3 slices of halloumi, and a pinch of salt and pepper to taste.
(Optional) Wrap the bagels tightly in parchment paper (or wrapping paper) so it’s all contained. To wrap the bagel, get a square piece of parchment paper/wrapping paper and then place the bagel in a corner. Then, fold the paper over the bagel from the corner on a diagonal until it’s all wrapped. Then, tuck the flaps under the bagel or use a piece of tape to tape the flaps to each other. Finally, cut the bagel in half. See the photos in the article for reference.