Whisk together the yogurt, sugar, salt, and vanilla until fully combined and the sugar is dissolved, with no gritty texture left.
Pour into a shallow, freezer-safe pan. Freeze for 90 minutes total, stirring every 30 minutes (3 times), scraping the sides and folding in any frozen bits each time.
While the base freezes, combine the cherries with the sugar, lemon juice, and vanilla in a bowl. Let sit for 60 minutes so the cherries release their juices and form a light syrup.
Once the 90 minutes are up and the base has started to firm, gently stir in the chocolate, if using.
Strain the cherries, reserving the syrup (nice drizzled on top or in a drink). Gently scatter the drained cherries over the surface of the base, keeping streaks and chunks rather than fully mixing them in — you want the vanilla base color to still show through.
Cover the pan with parchment or plastic wrap, pressing it directly onto the surface. This sets the cherry layer and helps prevent ice crystals.
Freeze until completely firm, about 2-4 hours total, depending on your freezer and pan size.
Let sit at room temperature for a few minutes before scooping and serving.
Note: since this is a no-churn method, the texture will be a bit icier than traditional churned frozen yogurt, but still delicious. It melts fast on a hot day, so serve promptly.
Leftovers should be stored in an airtight container in the freezer; the yogurt is best consumed within 3-4 days.
YIELD: 1 pint (2 cups)