Step 1
Combine mangoes, ginger, jalapeño and water in a blender or canister of a hand-held blender. Blend until smooth, about 1 minute.
Step 2
Set a fine-mesh strainer in a medium mixing bowl. Strain mango purée through strainer, using a flexible spatula to help push mixture through; discard solids left in the strainer.
Step 3
Pour half of the strained purée into a large jug (the mixture will froth up once you add the soda and lager). Top with half the lager and half the lemon-lime soda.
Step 4
Stir and taste. If you like the way it tastes, add the rest of the purée, followed by the rest of the lager and soda to maintain the same mango purée to lager to soda ratio. Alternatively, add remaining purée, lager, and lemon-lime soda in proportions that accord more with your taste.
Step 5
To serve: Pour into chilled glasses and top with a squeeze of lime juice. Garnish with a lime slice, if you like, and serve immediately.