It depends on what you mean by “Theory of Evolution”. As @Mariah has noted, that evolution occurs is a fact; we know it to be true, as it can be demonstrated with certain rapid-generation life forms, including fruit flies and plants. That’s as factual as facts can be.
But the “Theory of Evolution” is subtler than the factual question of “does evolution occur or not?” Darwin’s theory was predicated on “natural selection” of the advanced ability to survive (and reproduce) of certain members of various species based on naturally-occurring mutations, an idea that all life is related and springs from a common origin, that complexity evolves from simplicity and many other related ideas.
Not every single facet of evolution has been proven in a way that we can say “we know” how, when and why it occurs. (Because there are scientific and real questions still out about “punctuated equilibrium” and other fine points of the Theory.)
So, yes: evolution occurs. No shit. But Theory of Evolution is… you’ll have to pardon the pun here… evolving science.