Place a pan on medium-high heat and add oil and onions. Saute until the onions become translucent.
Add the ginger-garlic paste and saute for 30 seconds.
Then add the pureed tomato along with all the spices - salt, red chili powder, turmeric powder, cumin powder. Saute for 1 minute.
Add the washed red lentils along with 2 cups of water. Give it a stir. Reduce the heat to medium, cover and let it cook for 10 minutes.
Turn off the heat. Sprinkle garam masala and lemon juice.
Serve hot with rice or roti.