Easy, Fresh n Healthy Tabbouleh

Ingredients:
1 cup chicken/vegetable stock
1 cup water
1/2 cup fresh lemon juice, divided
1/3 cup plus 2 tablespoons olive oil, divided
1 1/2 cups couscous
1 seedless cucumber, cut into 1/4-inch pieces, plus cucumber slices for garnish
9 ounces cherry tomatoes, sliced in halves
3/4 cup finely chopped scallion
1 teaspoon kosher salt
a few grinds pepper
2 cups loosely packed fresh parsley leaves, minced
1 cup loosely packed fresh mint leaves, minced, plus mint sprigs for garnish