Mix the ground beef with paprika, chili powder, black pepper, garlic powder, and salt until evenly combined.
Sandwich the beef between two sheets of parchment paper and roll into an even thin layer, leaving a little margin at one edge. Remove the top parchment and roll the meat into a tight log from the long side.
Transfer the meat roll to a baking sheet. Add the whole garlic bulbs and tomatoes to the same sheet. Lightly drizzle the garlic with olive oil.
Bake for 40 minutes at 200°C.
Remove from the oven and let cool for about 15 minutes.
Make the tzatziki: squeeze the roasted garlic cloves from their skins and mash. Stir together the yogurt, mashed garlic, dill, mint, grated cucumber, lemon juice, and olive oil. Season with salt and pepper, then mix or blend until smooth.
Remove the cooled meat from the parchment and tear or slice into small pieces. Peel the tomato skins if desired.
Spread tzatziki on each flatbread, add optional cucumber, meat, onion, and roasted tomatoes. Roll up tightly and serve.