Preheat An Oven To 475 Degrees F (245 Degrees C). Grease A 1 1/2 Quart Glass Baking Dish With A Lid. Spread About 1/4 Cup Of Marmalade In The Bottom Of The Prepared Baking Dish. Set The Duck Breasts In The Dish On The Marmalade. Poke Holes All Over The Breasts With A Fork, And Spread A Layer Of Marmalade (About 1 Tablespoon For Each) Over The Duck Breasts. Sprinkle The Garlic Over The Top Of The Duck Meat. Spread The Onion And Orange Slices Around The Duck Breasts In The Dish. Cover The Dish, And Bake In The Preheated Oven Until The Duck Breasts Measure 100 Degrees F (38 Degrees C) When Measured With An Instant-Read Meat Thermometer, About 15 Minutes. Remove The Lid, Spread About 1 More Tablespoon Of Marmalade Over Each Breast, And Return To The Oven, Uncovered. Bake Until The Meat Is Medium Rare (145 Degrees F (63 Degrees C).