In a wet sump system, oil bubbles are usually due to over fill, and crank webs are whipping up the oil. Don't think that can happen in a dry sump system though, as on a Tuono. I've read the oil pump can cause bubbles, even on a dry sump system, especially if engine run at high revs such as when racing.
Were you riding the engine hard?
Have you checked the oil level yet, with oil at normal running temperature (not just a hot engine)?
New/good oil was anti foaming agents. If oil is old these could be breaking down.