There are many, but here's one from Wikipedia.
One example of evolution at work is the case of the hawthorn fly, Rhagoletis pomonella, also known as the apple maggot fly, which appears to be undergoing sympatric speciation.[19] Different populations of hawthorn fly feed on different fruits. A distinct population emerged in North America in the 19th century some time after apples, a non-native species, were introduced. This apple-feeding population normally feeds only on apples and not on the historically preferred fruit of hawthorns. The current hawthorn feeding population does not normally feed on apples. Some evidence, such as the fact that six out of thirteen allozyme loci are different, that hawthorn flies mature later in the season and take longer to mature than apple flies; and that there is little evidence of interbreeding (researchers have documented a 4-6% hybridization rate) suggests that sympatric speciation is occurring. The emergence of the new hawthorn fly is an example of evolution in progress.
There was also a study of some moth or butterfly in , I think England, during the industrial revolution.
It was mostly gray with some black but as the years went by and coal soot covered cities it’s coloration changed to mostly black with only small gray areas.
Umm, flies switching food supplies is not significant change.
More like the fly turning into something completely different, like a spider or something radically different.
You know, a real CHANGE, not changing diet.