Slice 2 of the tangerines into 1/2-inch thick wheels. Remove any seeds and then mist all over with the cooking spray.
Place a large skillet over medium-high heat. Working in batches, add the tangerine wheels in a single layer. Cook until lightly charred and caramelized on both sides, about 30 to 60 seconds per side. Repeat with the remaining wheels and then using tongs, carefully transfer to a parchment-lined plate and place in the fridge while you prepare the drink.
Slice the remaining tangerine into thin wheels and add them to a large pitcher or punch bowl. Add the tangerine juice, orange bitters, and half of the mint leaves. Stir to combine and chill until ready to serve.
When you’re ready to serve, slowly pour in the ginger beer and champagne and float the charred tangerine wheels and remaining mint leaves on the top. Ladle into glasses, garnish with a charred tangerine wheel and a mint sprig and serve.
