Make the crispy onion topping.
Sprinkle the onion rings with salt, then toss them in the flour to coat. Shake off excess flour.

In a large skillet, heat the cooking oil over medium-high heat, cook the onion rings, stirring often, until they turn a nice caramelized brown. Onions must be crispy, but not burned (15-20 minutes).

Make the Tomato Sauce.
In a saucepan, heat 1 tbsp cooking oil. Add the grated onion, cook on medium-high until the onion turns a translucent gold (do not brown). Now add the garlic, coriander, and red pepper flakes, if using, and saute briefly until fragrant (30-45 seconds more).

Stir in tomato sauce and pinch of salt. Bring to a simmer and cook until the sauce thickens (15 minutes or so).

Stir in the distilled white vinegar, and turn the heat to low. Cover and keep warm until ready to serve.

Make the Koshari
Cook the lentils. Bring lentils and 4 cups of water to a boil in a medium pot or saucepan over high heat. Reduce the heat to low and cook until lentils are just tender (15-17 minutes). Drain from water and season with a little salt.

Now, for the rice. Drain the rice from its soaking water. Combine the par-cooked lentils and the rice in the saucepan over medium-high heat with 1 tbsp cooking oil, salt, pepper, and coriander. Cook for 3 minutes, stirring regularly. Add warm water to cover the rice and lentil mixture by about 1 1/2 inches (you'll probably use about 3 cups of water here). Bring to a boil; the water should reduce a bit. Now cover and cook until all the liquid has been absorbed and both the rice and lentils are well cooked through (about 20 minutes). Keep covered and undisturbed for 5 minutes or so.

Now make the pasta. While the rice and lentils are cooking, make the pasta according to package instructions by adding the elbow pasta to boiling water with a dash of salt and a little oil. Cook until the pasta is al dente. Drain.

Cover the chickpeas and warm in the microwave briefly before serving.

Put it All Together!
To serve, fluff the rice and lentils with a fork and transfer to a serving platter. Top with the elbow pasta and 1/2 of the tomato sauce, then the chickpeas, and finally 1/2 of the crispy onions for garnish. Serve, passing the remaining sauce and crispy onions separately.