Whisk 3/4 cup orange juice with the orange zest, oil and brown sugar. Add smashed garlic to the mix.
Pound chicken to equal thickness and then add it to the orange juice mix. Marinate 2-4 hours.
Heat grill to medium high. Add chicken to the grill. Cook for about 4 minutes on each side (depending on thickness). While chicken cooks, take remaining orange juice and reduce it over high heat on the stove until it is thick and syrupy. Using kitchen shears, cut green onions into small pieces. Place grilled chicken on a platter, drizzle orange sauce over the top and sprinkle with chopped green onions.
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