Bifteki Burger Sandwich

Name: Bifteki Burger Sandwich
Ingredients: 1 cup shredded cucumber, seeds discarded; 2 cups plain Greek yogurt (see Cook's Notes); 2 to 3 cloves garlic, minced; 6 sprigs fresh dill, chopped; 3 tablespoons white wine vinegar; 4 tablespoons extra-virgin olive oil; Salt and pepper, optional; 1 1/2 pounds ground beef, 15 to 25-percent fat (the fattier, the tastier); 1 medium red onion, finely chopped; 35 fresh mint leaves, chopped; 1/2 pound manouri cheese, crumbled, or feta cheese; 2 long baguettes, each one cut into 3 equal pieces, sliced open; 1 to 3 tomatoes, depending on type or size, sliced; 1 medium red onion, thinly sliced; Salt and pepper; Spanish smoked paprika, optional