Mix the wine, vinegar, garlic, lemon zest, rosemary, salt, juniper berries, fennel seed, red pepper flakes, and black pepper to make a marinade.
Heat 3 Tbs. of the olive oil in a 12-inch skillet over medium-high heat until very hot. Add the mushrooms and cook, stirring once or twice, until golden brown on one or two sides, 1-1/2 to 4 minutes, depending on the type of mushroom—they should not be cooked all the way through. Spread on a plate to cool.
Add the marinade to the skillet. Bring to a boil, reduce the heat, and simmer for 5 minutes to infuse the flavors. Put the mushrooms and marinade in a heatproof container, such as a 1-quart Pyrex measuring cup. Let cool to room temperature, cover, and refrigerate overnight.
Drain the mushrooms, reserving the garlic and discarding the marinade and most of the aromatics (it’s OK if some of the aromatics stick to the mushrooms). Pack the mushrooms and garlic into a pint jar with lid (or other sealable container). Add enough of the remaining oil to cover, and refrigerate at least overnight and up to 1 month.