From Jonathan Payne, try this Arithmagon Generator. This is very simple to use and would be an ideal lesson starter. I like the option to use fractions, also to mix the question types as you see in the image. It is possible to choose missing sides, mixed or missing vertices.
This has been added to my Arithmagons collection which includes all the arithmagons you could ever want from the simplest to complex numbers and Calculus for older students!
Also from Jonathan Payne, many more lovely question generators, try his Missing Angles question generator which has numerous options including Algebraic questions.
Jonathan’s collection of generators is here.
On the subject of question generators, we can turn to another Jonathan! Jonathan Hall’s Mathbot.com has a wonderful collection of resources including question generators. His Differentiated Questions include numerous topics including several recent additions on Indices. These generators as you can see from the menu options can be customised to suit your class. They are also useful for student self-study.
Finally, from not a Jonathan, but John Tranter on Transum, this Custom Starter allows teachers to select the number of questions and the topics to include; scroll down the page and choose the topics you want from the Concept Selection.
It is possible to save a particular selection of topics as the URL for your selection will be generated. It is also possible to drag the panels so your questions are displayed in the desired order.
The beginning of a lesson can be a good time to review previous learning, starters like these can be ideal. On the very important subject of reviewing previous learning, see Retrieval Practice.