3 feta burgers grilled sourdough Recipes

lean ground beef, salt, divided, black pepper, divided, feta cheese, cut into 4 (1/2-oz) pieces, thick) red onion slices, extra virgin olive oil, divided, crusty sourdough bread slices, coarse-grained dijon mustard, plum tomato slices

tomatoes, seeded and diced, diced red onion, red peppers, grilled , seeds removed, crumbled feta cheese, red wine vinegar, cracked black pepper , or to taste, freshly chopped oregano leaves, extra-virgin olive oil, minced garlic, salt , or to taste, pepper , or to taste, portobello mushroom caps, stems and gills removed, sourdough rolls, split in 1/2, spring mix greens