first of all roast the suji in pan or kadhai for few minutes. Continuously stir the sooji while roasting. After roasting it, keep it aside in a plate.
Heat the oil in the pan. And add mustard and cumin seeds in it. When they splutter add the black lentil without skin, chickpeas lentils, curry leaves, and green chilies in it. Cook it until lentils are a little bit golden brown.
Add chopped onion and fry it until it turns pink. Now add sugar in it (Sugar is optional)
Now add tomatoes, salt, and red chilies powder and cook it nicely.
Add all the vegetables like capsicum, peas, etc. Cook these for 2-3 minutes.
Now add slowly add suji and water simultaneously while stirring the suji.
Cook it for 2-3 minutes on slow flame. Upma is ready.
You can garnish it with coriander if you want. It is an optional step.