I like passing the mushrooms through a meat grinder set up with the largest holes. This produces a mixture of mushrooms that's close to ground meat. If you don't have a meat grinder, you can get a similar texture by pulsing the mushrooms in a food processor, or by mincing them up with a knife.  When you bite into cooked ground meat, the liquid it releases contains a mixture of amino acids, fat, and collagen. The first gives the meat taste, and the latter two increase the viscosity of the liquid, which is perceived as richness. To replicate this with the ground mushrooms, I marinate them in a combination of soy sauce and rice wine, which both contain loads of amino acids. Then I add potato starch to the mixture, which helps bind the flavor ingredients into the mushrooms while making the liquid more "rich."