Combine water, red lentils, yellow split peas, salt, garlic, ginger, and red chile peppers in a pressure cooker. Close cooker, bring to high pressure according to manufacturer's instructions, and cook until split peas are tender and dal is thick, 6 to 10 minutes.
Remove cooker from heat and release pressure through natural release method according to manufacturer's instructions.
Heat ghee in a skillet over medium heat. Add mustard seeds; cook until they pop, 30 seconds to 1 minutes. Add onion; cook and stir until golden, 8 to 10 minutes.
