Season chicken with salt, pepper, thyme and orange zest; place in a large zipper-topped plastic bag then pour orange juice and champagne on top.
Seal bag and turn to combine ingredients; refrigerate overnight or for at least 4 hours, turning occasionally.
Heat the olive oil in a large skillet over medium-high heat; add marinated chicken (reserving marinade) and cook for 4 to 7 minutes per side or until cooked through, basting occasionally with a little marinade during the first half of cooking time, if desired.