The problem with meat substitutes is that they are substitutes. Without chemical help, it's nearly impossible to achieve a flavour in meat substitutes which is comparable to meat. However, putting this aside, there are viable options which look and have a similar structure like meat.
One thing I have seen used often are soya granules. By putting them together with water (some instructions), they slightly expand and mesh with each other which results in a structure that is comparable to ground beef / minced meat. Advantages are, among others, the relatively low price and a preparation time comparable to meat.
An exotic alternative is jackfruit which looks like pulled pork if prepared properly. In the department of fruit substitutes, there also is coconut pulp which has a similar structure to meat.
On the other side where the vegetables reside, eggplants and cauliflower can be used. The first one has a weak natural flavour which can be easily changed to one's desire. The second one can mimic meat quite well (see a recipe).
You could also use nuts. By grinding them into a fine powder, adding eggs and a binding ingredient of your choosing (flour, steeped bread bits, soya flour / granules, etc.), you can make patties and fry them regularly in a pan.
A lot of inspiration can be taken of the corresponding Wikipedia article listing possible meat substitutes, however not all listed are a good visual substitute in terms of texture and structure. (And as soon as it's possible, it might be worth taking a look at cultured meat.)
Summarising, there are a lot of good alternatives for meat. You should just bear in mind that right now it's not really possible to perfectly imitate the flavour of meat with natural means - but if this isn't your goal, then don't feel restricted and just cook away.
On a side note, I also have good experiences with deep-frying possible meat substitutes. By forming patties out of cheese and deep-frying them, you have a patty form with the extra that the cheese inside is very creamy due to the high heat of the deep-fryer. (In my experience, as soon as something is deep-fried and has this look, most people can ignore the fact it's a substitute and are eager to dig in.)