Hi Amp1022, welcome to EvC Forum!
I'm not sure, but you may possibly be asking the wrong question. Evolution proceeds by minute changes from one generation to the next. Offspring differ from parents in only the most superficial of ways. There is no point in time where a catfish, frog or termite lays eggs from which hatch enormously different creatures like seagulls, sloths or turtles. If you're skeptical of evolution because you believe it asserts that transformations of this magnitude can happen in a single generation, then rest assured that it asserts no such thing. In fact, the theory of evolution pretty much rules out anything like that ever happening.
Since evolutionary change proceeds in tiny steps, it follows that a new species differs little from the old. Red squirrels, gray squirrels, flying squirrels, they're all different species, and they all evolved from a common ancestor that differed from them in only small ways, as they differ from each other in only small ways.
So when you ask us to "describe one of the millions of examples of one species evolving into a completely different species," we can't describe anything as spectacular as a catfish evolving into a seagull because the differences between closely related species will always be small. We can only provide evidence of things that have actually happened. Gradual change is what happens, so that's all we can provide evdience for. Closely related species will always differ in only small ways.
I guess the most important point I should make is that I'm sure we're all just as firmly convinced as you are that we'll never find evidence of anything like catfish becoming seagulls.
--Percy