In a large bowl or glass measuring cup, combine sweetened condensed milk, limeade, tonic, gin, lime juice and lime zest. Whisk until smooth and fully combined. Divide mixture among 12 cups.
Insert a wooden spoon or popsicle stick into the centre of each lime slice and top on each cup, making sure there is no room between the mixture and lime slice.
Freeze until solid, at least 5 hours and up to overnight.
When ready to serve, cut open the cups and peel them away from the pops.