Cut peppers into quarters, remove seeds and white pulp. Run through juicer. Pour juice into small, low-sided skillet or saute pan, whisk over medium heat until bubbling around edges. Add slurry and cook, whisking to desired consistency; don't cook too long. Whisk in red wine, remove from heat. Add green onion, whisk in gently. If using, whisk in butter until blended; serve.