Add the lime juice, tequila, ice cubes, and sweetener into the blender.
Secure the lid and blend on high speed for about 30-45 seconds until the mixture is smooth and icy, with a slushy texture resembling shaved ice.
Stop the blender and check the consistency; if it’s too thick, add a splash of lime juice or a little more tequila and blend briefly again.
Pour the frozen margarita slushie into chilled glasses, letting the icy liquid mound slightly above the rim.
Garnish with lime wedges or salt rims if desired, then serve immediately for a refreshing, icy treat.