Use plain old javascript in your submit button, so your code in your view will look like:
....
<input type="submit" id="insert" value="Submit" name="Submit"
onclick="return confirm('Are you sure you want to submit')">
</fieldset>
}
Note: There are other ways of doing this, but this is the quickest and simplest, and also the dirtiest.
Also see:
How can I add a client-side (JavaScript) confirmation message box using ASP.NET?
for how to add it as validation.