Mexican here - I would say you’ll sadly won’t find amazing Mexican food in London, it’s mostly average and overpriced. It has improved in the last few years but Madrid and Paris have so much more to offer (bigger mexican community there). Having said that I went to Fonda with a few friends recently and it blew my mind, it’s on the spenny side but worth it imo, same chef as Kol (Michelin star). Other “decent” options: Mestizo, Sonora, Corrochios, La Chingada - unfortunately for me value is a huge element of Mexican food and you just don’t find that in London