4 sprigs tarragon plus 2 tablespoons minced leaves
2 large shallots, 1 halved, 1 minced
2 garlic cloves, 1 smashed, 1 minced
1 pound skinless, boneless chicken breasts
Kosher salt, freshly ground pepper
3/4 cup plain Greek yogurt
3 tablespoons olive oil
1/2 pound thinly sliced stringed sugar snap peas
1 cup shelled fresh English (or frozen, thawed) peas
1/2 cup thinly sliced stringed snow peas
1/4 cup finely chopped flat-leaf parsley
1/4 cup finely chopped fresh chives
2 teaspoons finely grated lemon zest plus 1 tablespoon (or more) fresh lemon juice
8 slices toasted whole grain bread and/or lettuce leaves