Pre-heat oven to 400 F°(200°c).
Line a baking sheet with parchment paper.
In a sauté pan, heat 2 tbsp (30mL) of melted butter over medium heat. Sauté onions until they start to caramelize (approx. five minutes). Remove from heat and set aside.
Combine the garlic with the remaining melted butter. Gently brush the butter onto one quarter sheet of fillo pastry. Layer with another sheet and brush with butter. Repeat this process until four quarter sheets are layered together.
Place 1/8th of the caramelized onions in the center of the square and top it with ½ cup of tomato halves, 1/8th of the olives and 2 tbsp. of crumbled feta cheese. Gather the edges over the tomato mixture, pleating as you go all the while leaving the center open.
Brush the outside of fillo with butter and carefully place the newly formed galette onto the baking sheet with the aid of a large lifter or flat spatula.
Bake for 15 to 20 minutes or until golden.
Serve with a side salad for a light lunch or as a great starter!