Prep breadcrumb topping. In a small bowl, stir together the breadcrumbs, 1 teaspoon olive oil, dried oregano, and a pinch of salt. Set aside.
Preheat broiler. Position oven rack 5 to 6 inches away from the broiler; preheat.
Sauté shallot. Heat the remaining 1 tablespoon olive oil in a cast iron skillet or other nonstick, oven-safe skillet over medium-low heat. Add the shallot and cook until softened, around 3 minutes.
Prepare egg mixture. While the shallot cooks, whisk eggs, milk, parsley, dill, and Dijon until well blended. Stir in 1/2 cup crumbled feta and season with ground pepper.
Add egg mixture to shallots; cook. When the shallots are softened, add the egg mixture to the skillet. Increase heat to medium and cook, without stirring, until the bottom is set and the edges are just starting to firm, around 5-7 minutes; the top should still be slightly runny.
Top with tomatoes, remaining feta, and breadcrumbs. Remove skillet from heat and place tomato halves, cut side up, evenly across the top of the frittata. Sprinkle remaining 1/4 cup feta around the tomatoes. Sprinkle the breadcrumbs evenly over the top of the entire frittata.
Broil. Place the skillet under the broiler and cook until the eggs are set on top and the breadcrumbs are golden, 1-3 minutes. Watch closely to make sure the topping doesn’t burn.
Rest, then serve. Remove the frittata from the oven and let rest for 2-3 minutes. Run a spatula around the edge to loosen, slice into wedges, and serve.