Squash and Lentil Salad

Name: Squash and Lentil Salad
Ingredients: 1 small butternut squash, halved lengthwise, seeded, and cut into 1/2-in.-thick half-moons; 1 large red onion, cut into 1-in. wedges (root end left intact); 5 Tbsp. extra-virgin olive oil, divided; 1 1/4 tsp. kosher salt, divided; 3/4 tsp. garam masala, divided; 8 dates (preferably Medjool), pitted and sliced; 2 Tbsp. apple cider vinegar; 1 8-oz. pkg. microwavable black lentils (such as Good & Gather), cooked according to pkg. directions and cooled, or 1 (15-oz.) can green lentils, drained and rinsed; 2 cups packed arugula; Lemon wedges, for serving