Just doing B.Tech. and M.Tech. in engineering would not help in getting a lecturer/Assistant Professor post in UG/PG colleges but there are some ways to achieve this ambition and that is that after doing B.Tech. one can think of doing M.Sc. Physics and many institutes allow that and give admission to B.Tech. students in Physics. So, once one does M.Sc. Physics then one can go for NET test and after qualifying that one is eligible to apply for the lecturer/Assistant Professor post. There is another option which is actually a still longer route that one can do even PhD after M.Sc. and then one need not to go for NET and directly apply for the position.
Some of the institute like Central University of Haryana; Indian Institute of Space Science and Technology, Thiruvananthapuram; University of Pune; Lovely Professional Univesity; University of Delhi; Jawaharlal Nehru University; Tata Institute of Fundamental Research; Inter-University Center for Astronomy and Astrophysics, Pune take engineering gradutes also in M.Sc. Physics. You can think of that in case you decide to go for M.Sc. in Physics.
Some reputed institutes like IITs, ICTS Bangalore, HRI Allahabad, IMSc Chennai, TIFR Mumbai, TIFR Hyderabad, IISERs, HCU, Pune University etc consider the admission for M.Sc. Physics based on the scores exams like JAM, TIFR GATE, JEST etc and that option can also be explored.
If you want to go for M.Sc. Physics then I would advise you to go through some online Physics tutorials of UG level so that you do not have any difficulty in coping up with the syllabus of the M.Sc. Physics.
Knowledge is power.