Line a rimmed baking sheet with parchment or waxed paper. Peel bananas and insert a craft stick about halfway into each one. Set bananas on baking sheet and freeze until well chilled, about 20 minutes.
Combine chocolate chips and oil in microwave-safe bowl and microwave on high until just melted, 1 to 2 minutes (stir every 20 seconds). Stir until smooth. (Or place chips and oil in a heatproof bowl and set over a pan of simmering water to melt.)
Place sprinkles, nuts, coconut or Heath bar bits in a shallow bowl. Use a thin metal spatula to coat each banana with chocolate. Working over topping bowl, sprinkle each coated banana with topping. Place bananas back on baking sheet and freeze until chocolate is firm, at least 30 minutes and up to 1 day.