Yes, lentils are a decent substitute and quite healthy. I also tried soy chunks that you soak in broth for some time before adding to the sauce. These will benefit from a lot of time in the sauce and then are quite nice and a bit chunkier than lentils.

Neither will be as good as the original ground pork/beef that goes in a proper Italian bolognese. But I do like both versions enough to make a meat free version 8/10 times

I can't speak to using lentils as a meat replacement but lentils go hard with rice. Another good way to add nutrients to a rice bowl is to throw in some quinoa and cook it with the rice. I basically have a carb, meat, and preferably fresh veg but yea it can get repetitive. I've found you can make the same meal but make it taste incredibly different by playing with seasonings and salt. Make a sweet and sour chicken one night and spicy next for example. My local grocer has some really cheap meat sometimes that's like about to go bad so sometimes that's a good buy. Unfortunately meat prices are on the rise, try tofu some time. if you dry it out properly and use some gochujang sauce and fry it up in some corn starch it will crisp up nicely and goes HARD in a rice bowl. You can cut meat out of a few meals to save some dough and use protein rich beans and/or nutritional yeast (has all the proteins we need so if your worried about missing something from the meat it's a good additive)