While I'm not clear why you would want to go back to an undergrad given your education, I would look for programs with names like "Computational Mathematics" or "Computational Science". I earned a Bachelor of Mathematics in Computational Mathematics. The first two or three years were heavily focused on the mathematical foundations (eg. non-linear and discrete optimization, combinatorics and CS fundamentals, statistics and applied mathematics). The latter half of third year and all of fourth year were basically a "create your own adventure" where you could focus on subject areas that interested you (ex. econometrics, computational biology, industrial engineering, computational statistics + machine learning, etc). We had a breadth requirement t that often pushed people to obtain a minor from a different faculty (eg. Arts or Sciences). The program overview for my school might give you an indication of what content to look for [1].
You might also find graduate level programs that are similar in aim; my school also offers an MMath in Computational Mathematics [2].
1. http://ugradcalendar.uwaterloo.ca/page/MATH-Computational-Ma...
2. https://uwaterloo.ca/computational-mathematics/future-master...