My suggestions: we do our weekly menus basically like this: 1 day of chicken, then beef, then pork (this could be anything from pork chops with a blackberry & port wine sauce to red beans & rice with sausage), then vegetarian (moussaka, lasagna, or sweet potato gnocchi and sliced squash, peppers, and mushrooms in a pasta sauce?), then fish (even fish tacos! Broil some fish marinated in lemon or lime juice, a little salt and pepper, and then break it up in a tortilla and serve it with fresh chopped vegetables and avacado), then a soup or stew, and another day for leftovers (whatever's left). That's a week, and it keeps it a bit varied instead of the same stuff day after day. I do get in ruts and do have to make steps to break out. One thing we do like to do is go to the farmer's market on Thursday afternoons after naptime. We pick a different vegetable every week and experiment with it. As for beans, there are lots of different kinds of beans, and lots of ways to make them.
As for the taco question: my kids started eating soft tacos before their first birthday. Crunchy tacos: when they're old enough to eat a chip, they're old enough to eat tacos (albeit a messy meal). What's not to like? Ground beef, cheese, avocado (one of both boys' very first foods), a little hot sauce if you want and if not then some chopped tomato, and some lettuce. I just chop half an onion, brown it with a pound of meat, drain, use Old El Paso taco seasoning (McCormicks is very bland). We really just serve them the food we eat. The only difference is that I don't make things QUITE as spicy as I used to, where we can just add some LA Hot Sauce afterwards to ours (or use regular rotels instead of extra hot). When this is different: if we're making something like smothered filet mignon topped with gorgonzola, I'll serve the boys some sirloin instead because the filet is kinda wasted on them....and they don't like gorgonzola very much. (Though they love feta!) Just experiment. I'm sure you have obstacles at mealtime, but even picky eaters can learn to taste things and enjoy eating.