Sambar South Indian Vegetable Stew

Name: Sambar (South Indian Vegetable Stew)
Ingredients: ½ cups toor dal (yellow pigeon peas), rinsed, soaked 30 minutes, and drained; ½ cups coconut or canola oil; 8 cloves garlic, mashed into a paste; 1 small red onion, cut into 1″ pieces; 1 (2″) piece ginger, peeled and mashed into a paste; 4 small green Thai chiles or 2 serranos, chopped; 2 drumsticks, trimmed and cut into 2″ pieces; 2 medium carrots, quartered lengthwise and cut into 2″ pieces; 2 medium Yukon Gold potatoes, peeled and cut into 1″ pieces; 2 plum tomatoes, chopped; ½ cups sambar masala; 3 tbsp. fresh or frozen grated coconut; 3 tbsp. tamarind paste; 1 tbsp. ground cumin; 1 tsp. ground turmeric; 10 small okra, trimmed and halved crosswise; Kosher salt, to taste; 2 tsp. black mustard seeds; 10 fresh or frozen curry leaves; 5 chiles de árbol; ¼ cups cilantro leaves; Cooked white rice, for serving (optional)