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. (Note: when the lentils are ready, they should not be fully cooked. They should be only par-cooked and still have a bite to them as they need to finish cooking with the rice).
• 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.