Halve baguettes lengthwise. Peel and halve onion. Slice half the onion into thin strips (julienne) and finely dice other half. Mince dill (dill stems are tender and can also be minced). Trim cucumber and cut into 1/4" dice. Zest lemon, halve, and juice. Cut Roma tomato into 1/4" dice. Drain and rinse artichokes. Halve olives.

Combine yogurt, half the cucumber, dill (reserve a pinch for garnish), 2 Tbsp. lemon juice, 1/2 tsp. salt, and 1/4 tsp. pepper in a small bowl. Mix together thoroughly and refrigerate until ready to use.

Combine remaining cucumber, finely diced red onion, tomatoes, red wine vinegar, lemon zest, 2 tsp. olive oil, 1/4 tsp. salt, and a pinch of pepper in a small bowl. Mix together and refrigerate until ready to use.

Place baguette halves on prepared baking sheet. Drizzle each piece with 1/2 tsp. olive oil. Bake 5-7 minutes, or until bread is golden brown. While bread toasts, heat 1 tsp. olive oil in a medium pan over medium-high heat. Place julienned onions in pan and cook 5-7 minutes, stirring constantly, until softened.

Evenly spread about 2 Tbsp. tzatziki sauce on each baguette. Add artichoke hearts, olives, caramelized red onions, and feta to each baguette.

Divide salad between two plates or bowls and serve with two tartines. Garnish tartines and salad with remaining dill. Serve extra tzatziki sauce on the side.