1 tablespoon extra-virgin olive oil, divided
1/2 cup chopped onion
2 garlic cloves, minced
1/3 cup old-fashioned rolled oats
1/3 cup sliced almonds, toasted
2 tablespoons cornstarch
1 1/2 teaspoons chopped fresh sage
2 teaspoons Dijon mustard
1/2 teaspoon salt
1/4 teaspoon freshly ground black pepper
2 (15-ounce) cans cannellini beans, rinsed and drained
1 large egg, lightly beaten
1/2 cup reduced-fat sour cream
2 tablespoons grated fresh onion
2 tablespoons crumbled feta cheese
3 (6-inch) pitas, cut in half
6 green leaf lettuce leaves
6 (1/4-inch-thick) slices tomato